Friday, January 09, 2015

An artist's conception of a black hole binary in a heart of a quasar,
with the data showing the periodic variability superposed. Credit:
Santiago Lombeyda, Center for Data-Driven Discovery, Caltech.› Larger image

The central regions of many glittering galaxies, our own Milky Way
included, harbor cores of impenetrable darkness -- black holes with
masses equivalent to millions, or even billions, of suns. What's more,
these supermassive black holes and their host galaxies appear to develop
together, or "co-evolve." Theory predicts that as galaxies collide and
merge, growing ever more massive, so too do their dark hearts.

Black holes by themselves are impossible to see, but their gravity
can pull in surrounding gas to form a swirling band of glowing material
called an accretion disk. When this process happens to a supermassive
black hole, the result is a "quasar" -- an extremely luminous object
that outshines all of the stars in its host galaxy, visible from across
the universe.

"Quasars are valuable probes of the evolution of galaxies and their
central black holes," said S. George Djorgovski, professor of astronomy
at the California Institute of Technology in Pasadena. "If we can
systematically study a large population of quasars, we can discover rare
and unusual phenomena that can help us better understand the overall
picture of their evolution."

In the Jan. 7 issue of the journal Nature, Djorgovski and his
collaborators, including Daniel Stern of NASA's Jet Propulsion
Laboratory in Pasadena, California, report on an unusual repeating light
signal from a distant quasar that they say is most likely the result of
two supermassive black holes in the final stages of a merger --
something that is predicted from theory but which has never been
observed before. The findings could lead to a better understanding of
black hole mergers and galaxy evolution, and also help shed light on a
long-standing conundrum in astrophysics called the "final parsec
problem." That refers to the failure of theoretical models to predict
what the final stages of a black hole merger look like, or even how long
the process might take.

"Until now, the only known examples of supermassive black holes on
their way to a merger have been separated by tens or hundreds of
thousands of light-years," said Stern. "At such vast distances it would
take many millions, or even billions, of years for a collision and
merger to occur. In contrast, these black holes are at most a few
hundredths of a light-year apart, and could merge in about a million
years or less."